This invention concerns window panels for use in automotive glazing. In recent years, automobiles often have been equipped with window panels having an opaque black out masking border used to conceal constructional details, such as adhesive beads, etc. The black out border also adds an aesthetic accent, and has typically been created by black paint or imprinting applied to a window glass perimeter. The blackout border also functions to block UV radiation in sunlight needed to protect the adhesive used to fixed the window panel against the degrading effects of UV radiation.
A refinement of such masking border has been to add a transition xe2x80x9cfade outxe2x80x9d treatment to a solid black perimeter band, comprised of a region of gradually decreasing opacity, which improves the aesthetic appeal of a masking border having only solid black band.
The fade out region has been produced by imprinting a dot pattern of decreasing density adjacent the solid black band.
It has long been proposed to utilize hardcoated molded plastic panels as a substitute for the glass panels traditionally used in automotive glazing applications in order to reduce vehicle weight, to improve safety, and to enhance design flexibility in the shaping of the window panels.
The relatively large sizes of the molded plastic panels typically required for automotive glazing applications may be limited by the tonnage of the injection molding machine. That is, the area of the panel multiplied by the pressure required to inject the plastic (i.e., 2 tons per square inch) must not exceed the maximum tonnage limit of the machine, i.e., 750 tons. It would be advantageous to circumvent at least to some extent the size limitations imposed by the tonnage limit of the molding equipment.
Another desirable characteristic of an automotive window would be an ability to create an exit opening from within the passenger space by allowing an occupant to be able to force the window panel out without compromising the required minimum structural integrity of the window.
It is an object of the present invention to provide an improved process for creating a black out border treatment for molded plastic window panels with a fade out region adjacent a more completely opaque band extending around the perimeter of the panel.
It is another object of the present invention to provide a process for increasing the maximum size of an injection molded automotive window panel over that size which would otherwise be imposed by maximum tonnage limitations of the injection molding equipment used.
It is yet another object to provide a window panel which allows an exit opening to be formed by pushing out a section of the window while maintaining adequate structural integrity of the window panel.
The above recited objects as well as other objects which will be understood upon a reading of the following specification and claims are achieved by constructing a molded plastic window panel in two pieces, a rigid inner transparent panel piece and a rigid outer surrounding piece, each piece having a portion thereof overlapping a contiguous portion of the other piece. The outer piece and inner piece are each molded from a suitable plastic resin such as polycarbonate, the overlapping portions bonded together to form a unitary rigid window panel.
The inner piece is molded from a transparent resin and is configured to be fit within the outer piece which is molded from a plastic resin pigmented or otherwise having a material characteristic producing a maximum opacity. Alternative to black pigments, various colored additive materials can be used (which could be completely opaque, transparent or translucent) which can also produce special effects, i.e., textured, metallic flakes, etc.
The overlapping portion of the outer piece is of reduced thickness, so that the n overlap joint produces a band of reduced opacity, providing a transition to the maximum opacity outer band.
The overlapping portion of the outer piece is preferably tapered to be of decreasing thickness, creating a fade out transition region with a gradual lightening of the masking opacity. The overlapping portions can have many different configurations.
As an added feature, the overlapping portions are bonded so as to establish a controlled failure mode at a predetermined level of an outwardly directed force, enabling separation of the inner and outer pieces. The separation of the inner piece from the outer piece fixed to the vehicle body structure creates an opening which may be used for escape or extraction of the vehicle occupants, while being much more resistant to inwardly directed forces since abutting the fixed outer piece.
The inner and outer pieces can be molded in a two shot process, which by the combination of the two pieces allows manufacture of a complete window panel of a size greater than that able to be molded by a one shot process at the maximum allowable tonnage capacity of the injection machine.